This invention relates to a fastener, preferably a one-piece plastic fastener, such as a rivet. It is well known in the art to provide a hollow fastener having a tapered internal bore passing through the head and shank for accepting a positively locked expander element. Such devices are found in the patents to Carno, U.S. Pat. No. 2,898,798; Rapata, U.S. Pat. No. 3,385,157 and Birmingham, U.S. Pat. No. 3,411,397. Each of these devices disclose a tapered internal bore in which the shank portions or prongs are radially expanded by a drive pin or screw, either separate or integrally molded, which when axially moved engages the tapered wall of the bore and radially expands the free ends of the shank portions or prongs outwardly beyond the surface of the apertured panel opposite the surface engaged by its head or against the side wall of a blind bore. The patents to Schuplin, U.S. Pat. No. 3,417,438 and Kearns, U.S. Pat. No. 2,542,144 are examples of fastening devices having impositive cam-like means located intermediate the extremities of the bore for impositively restricting movement of their expander element, while the patent to Rapata, U.S. Pat. No. 2,941,439 teaches the use of a resilient shouldered element carried by the extremity of the expander element for cooperative engagement with the ends of the prong sections.